In the underground mining of coal or other minerals, endless conveyor systems are used to transport the mined aggregate material won from the mine face to the surface for washing, dewatering, or other types of processing before it is ready for use. One type of conveyor commonly used is known as a stage loader. As well known in the art, the stage loader is a type of scraper chain conveyor that receives coal from an armored face conveyor as a part of a longwall mining machine and loads it onto a takeaway conveyor which eventually transports the coal to the surface. The scraper chain conveyor includes an upper deck supported by spaced sidewalls that define a feed path. To move the coal along this feed path, one or more heavy gauge chains are connected to pull a series of flight bars along the conveyor. A driven shaft having at least one sprocket is mounted at one end of the conveyor to drive the chain(s) and an idler shaft having a similar sprocket(s) is provided at the opposite end. Both ends of the conveyor include drive or idler support units for the respective shaft. These units typically include spaced support plates that project outwardly from the upper deck at the end of the conveyor frame. These support plates have semi-annular profiles that help in guiding the flight bars as the transition is made from the forward to the return run, or vice versa.
In the past, drive or idler shafts were commonly supported in bearing housings carried directly in the sidewalls of the conveyor frame. An example of one such early proposal is found in U.S. Pat. No. 4,037,713, issued Jul. 26, 1977. This patent discloses a conveyor with spaced apart sidewalls, each having a recess for installing a bearing housing. The housings receive and provide rotational support for the ends of the respective drive or idler shaft.
One significant limitation inherent in this "outboard" arrangement shown in this earlier patent (and others like it) is that access to the bearing housings is restricted. Furthermore, the conveyor frame for either the face conveyor or the stage loader (or other conveyor) is typically placed as close as possible to the mine face or other wall. This conserves space and, for an armored face conveyor, ensures that the coal won from the mine face falls onto the conveyor. This tight spacing further prevents the bearings from being easily reached for servicing on the side of the conveyor next to the face. Instead, the shaft and bearing housings together must be lifted upwardly out of the recesses in the conveyor frame. This is especially difficult in the confines of an underground mine. Such an arrangement makes not only servicing, but also inspection and/or lubricating the bearings extremely difficult and time consuming.
A more recent approach can be found in U.S. Pat. No. 5,232,068, issued Aug. 3, 1993, which discloses a conveyor frame having split sidewalls that contain bearing housings for rotatably supporting the ends of an idler shaft. As can be appreciated, the split sidewalls permit the drive or idler shaft to be more easily removed horizontally from the end of the conveyor, as may be necessary for servicing/repair or replacement. Additionally, a remote lubrication system is proposed to minimize wear on the shaft and lessen the frequency with which the shaft or bearings are replaced.
The '068 patent also provides other features designed to overcome the limitations inherent in the support arrangement disclosed in the '713 patent. However, it should be recognized that the shaft is still fully supported by the side walls of the conveyor frame. This means that the length of the shaft is dictated by the spacing of the sidewalls of the conveyor frame. In other words, because the shaft support is provided by the sidewalls of the conveyor frame, the shaft must be at least as long as the distance between the inner edges of these sidewalls. This not only increases the cost, but also prevents a drive or idler shaft from one conveyor from being interchanged with those used in different types or sizes of conveyors, as the spacing of the sidewalls of the conveyor frame frequently varies. Specialized shafts must be kept on hand for the many different types of armored face or scraper conveyors that may be used at a particular underground mining installation, which is obviously inconvenient and expensive. Moreover, if the shaft is damaged, worn out, or otherwise in need of replacement, significant and costly production downtime may result while a replacement shaft having a suitable length dimension is found or fabricated.
In an effort to overcome these limitations, others have proposed arrangements where the drive or idler shaft is supported by separate bearing housings mounted inside, or "inboard," of the conveyor frame sidewalls. One example of such an arrangement is shown and described in British Patent Specification No. 2,156,943, owned by Fletcher Sutcliffe. In this proposal, spaced bearing housings each include narrow projecting studs inserted in corresponding recesses formed in a face plate of the conveyor frame. By tightening a nut on the threaded end of each stud, the peripheral surfaces of the bearing housings are brought into engagement with the corresponding ends of upper and lower support plates projecting from the conveyor frame. The bearing housings can be spaced apart for supporting the ends of the shaft (FIG. 5), brought inward with the sprockets moved to the ends of the shaft (FIG. 4), or combined in a single center bearing housing (FIG. 6).
While this arrangement avoids the limitations created by supporting the shaft in the spaced sidewalls of the conveyor frame, it has several shortcomings. For example, the single stud mounting is very insecure and prone to failure in the harsh conditions and due to the tremendous forces that scraper chain conveyors are exposed to during normal operation. These forces include large deflection and twisting forces created by the rotation of the shafts as the heavy gauge chains are pulled or guided along by the sprockets. Over time, this tends to weaken or loosen the stud/nut fastener combinations securing the housings in place and could possibly lead to conveyor failure. It should also be appreciated that these fastener combinations are in a difficult place to reach below the upper surface of the conveyor. This complicates any preemptive servicing efforts and requires significant and costly production downtime in the event failure does occur.
The deleterious effects of the twisting forces are especially problematic in the embodiment having dual outer sprockets carried on the ends of the drive or idler shaft (see FIG. 5 of the '943 patent). The coaction of the chains on such spaced sprockets tends to create an uneven loading condition that eventually allows the stud to pivot back and forth in the recess. To resist this twisting force, the '943 reference proposes capturing the respective ends of the shaft in recesses or slots formed in the sidewalls of the conveyor frame. Of course, although this may offer some resistance against the troublesome twisting forces, it again makes the shaft length directly dependent on the spacing of the sidewalls of the conveyor frame.
Expressly recognizing the limitations of the above-described support arrangements, U.S. Pat. No. 4,953,692 to Stoppani et al. proposes a unitary central bearing housing mounted inboard of the conveyor frame sidewalls. Specifically, the '692 bearing housing includes a projecting nose for insertion in a receiving recess formed in the front of the conveyor frame. To seat this nose in the recess, an expansible fastener is inserted vertically through a single set of corresponding apertures extending through the nose and cross member. Once registered in the aligned apertures, expansion of the fastener is supposed to draw the bearing housing into engagement with the upper and lower portions of the cross member and hold it in this position.
Although the housings in this proposal provide support for the shaft independently of the conveyor frame sidewalls, limitations similar to those described above for the Fletcher Sutcliffe proposal remain. For instance, the uneven loading on the shaft created by the chains riding on the dual outer sprockets eventually tends to cause the fastener to loosen, which can allow the nose to pivot in the receiving recess. This back and forth movement over time can destroy the tight seating engagement due to wear on the seating surfaces in the recess, and thus possibly lead to a conveyor failure. Furthermore, the center bearing housing arrangement proposed in this patent would not be suitable for use with drive or idler shafts having inner sprockets.
Accordingly, a need is identified for an assembly for securely and reliably supporting a shaft in an endless conveyor of the scraper chain type that is commonly used to transport aggregate materials in underground coal mining. The assembly would support the shaft independent of the sidewalls that typically form a part of the conveyor frame. This independence would allow for shorter and consequently lighter shafts. Shafts could also be interchanged between conveyors having side walls spaced any distance apart, as long as this distance is greater than the length of the shaft. Additionally, a secure and reliable mounting for the shaft would enhance stability and resist twisting, deflection, and other large forces created as the chain(s) are pulled along or carried by the sprockets of the drive or idler shafts. However, the assembly would also allow the shaft to be easily accessed for maintenance, including dismounting for reversing or replacement, as may be necessary or desirable.